Recreate the OS390-Unix config target

Reviewed-by: Tim Hudson <tjh@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/5035)

CHANGES

@@ -9,6 +9,10 @@
 
  Changes between 1.1.1 and 1.1.2 [xx XXX xxxx]
 
+  *) Recreate the OS390-Unix config target.  It no longer relies on a
+     special script like it did for OpenSSL pre-1.1.0.
+     [Richard Levitte]
+
   *) Instead of having the source directories listed in Configure, add
      a 'build.info' keyword SUBDIRS to indicate what sub-directories to
      look into.

Configurations/50-os390.conf

@@ -0,0 +1,11 @@
+## -*- mode: perl; -*-
+(
+# OS/390 Unix an EBCDIC-based Unix system on IBM mainframe
+    "OS390-Unix" => {
+        inherit_from     => [ "BASE_unix" ],
+        cc               => "cc",
+        cflags           => "-O -DB_ENDIAN -DCHARSET_EBCDIC",
+        bn_ops           => "THIRTY_TWO_BIT RC4_CHAR",
+        thread_scheme    => "(unknown)",
+    }
+);